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 From:  "Chris Buechler" <CBuechler at strothman dot com>
 To:  "Steve Peterson" <steve dash hv at zpfe dot com>, <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] 1.0 and net4501 - dropped traffic
 Date:  Thu, 24 Jun 2004 12:15:16 -0400
> > Unfortunately, packet drops are the normal method of throttling data
> > flow.
> > If packets don't get dropped, TCP assumes it's not sending fast
enough
> > and
> > sends faster, limited only by the rate that the sender can produce
data
> > and the rate the receiver can consume it. 
>
> That's interesting.  I'm trying to reconcile that with the behavior I
saw
> when I used to run a stock FreeBSD 4.x distro on my old P90 as a
> firewall.  I could ping all day and never have a dropped packet.  Same
> thing at my parents' house with their Netgear WGT624.
>

The above explanation from Fred isn't exactly correct.  TCP *will* pass
data as fast as the sender can produce and the receiver can receive.
Dropped packets are by no means a method of throttling, and shouldn't
happen frequently if your connection is solid, which it sounds like it
is. 

I run a half dozen netmon graphs on my second screen constantly, behind
a m0n0wall box (netmon pings a given host and displays a graph in real
time http://www.nullsoft.com/free/netmon/).  Therefore, I see all
dropped packets.  It drops about 1-2% of pings, which I've found is
pretty typical for most any internet connection.   It's almost certainly
not m0n0wall that's dropping those either, it's something else along the
way.  Keep in mind ICMP is not a reliable protocol, so 1-2% loss on ICMP
over several internet hops is good, and would likely equate to 99.9+ %
success on TCP packets.  

A cause might be a machine behind the firewall with a virus that's
trying to flood traffic to the internet.  That could overload m0n0wall,
and/or your internet connection, which would cause dropped packets.
Losing 10% of your packets is not normal, and as a rough estimate, would
cause you to be wasting maybe as much as half of your bandwidth due to
retransmittals.  (% packet loss is a fraction of the % wasted bandwidth
- 30-40% packet loss makes for a completely unusable connection).  

-Chris


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